Let's see how much I've learned from reading the forums here. You are correct about the fabric weight. 3 yard,5 yard and 8 yard refers to the length of the fabric used in the kilt if it were laid out ( not pleated). The more fabric one starts with, the more ( and deeper) the pleats can be made.
Most of the posters here seem to prefer no longer than mid-knee. I like mine just above.
To those more experienced than I, please feel free to correct me and educate both me and the OP.